This application relates to gas turbine engines in general and in particular to methods and apparatus for regulating the flow of lubricating oil in a gas turbine engine.
Many applications for gas turbine engines involve the use of an engine driven gearbox or other accessories supplied with oil from an engine-driven oil pump. For example, a turbofan jet engine designed for use in aircraft typically includes a fan reduction gearbox coupled between the shaft of the gas turbine engine, which turns at a high rate of speed, and the turbofan shaft which must turn at a substantially lower speed. Such engine driven gearboxes are typically supplied with oil for heat dissipation and lubrication by a positive displacement oil pump, directly or indirectly driven by the engine shaft, in combination with an oil pressure regulator gear torque. Generally, the oil supply system is sized to ensure that the supply of the oil to the gears is sufficient to maintain proper operation at the maximum gear torque condition. Accordingly, at gear torque levels below maximum, the supply of oil to the gearbox exceeds that necessary to maintain the satisfactory operation of the gears. Moving parts within the gearbox churn the excess lubricant, thereby consuming energy and generating waste heat, which reduces engine efficiency and oil service life.
As disclosed in U.S. Pat. No. 4,569,196 issued Feb. 11, 1986 to Waddington, it has been suggested that engine efficiency could be increased by employing a flow reduction valve that operates to reduce oil flow as a function of the altitude at which the engine is operating. The altitude compensating flow reduction valve taught by Waddington recognizes that the power output of an aircraft engine, necessary to maintain stable flight, decreases with altitude. The valve taught by Waddington, however, does not actually measure engine load. Accordingly it does not adjust the flow of oil in direct relationship to engine load. Accordingly, what is needed, and what the prior art lacks, is an oil flow control valve that matches the flow of oil to the actual requirements of the lubricated units.